Method of manufacturing an automotive sound system

ABSTRACT

An automotive sound system achieves manufacturing flexibility by joining a common chassis which implements radio functions with additional boards that are specific to either a cassette, CD, or DAT mechanism which is to be joined with the radio as an integral unit. Each board is controlled by a microcontroller and the separate microcontrollers are connected by a shared bus.

This application is a division of application Ser. No. 07/288,606, filed12/22/88, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates in general to automotive sound systemsand, more specifically, to a distributed multiprocessor-basedarchitecture for improving manufacturability of such sound systems.

With the recent introduction of digital audio technology, automobileconsumers have been given a selection of automotive sound systems. Thus,a typical system comprises an AM/FM radio receiver combined with astandard cassette tape player, a digital compact disc (CD) player, or adigital audio tape (DAT) player.

Prior art systems have been designed and manufactured separatelyaccording to whether the system is a radio receiver/cassette, a radioreceiver/CD, or a radio receiver/DAT. With the advent of electronicradio tuning, digital displays, station search functions, etc.,designers have come to rely heavily on the microcontroller. Thus, amicrocontroller has been given control of radio functions and tape or CDfunctions in sound systems designed as integral units.

For example, U.S. Pat. No. 4,292,467, granted to Odlen et al., disclosesan audio receiver in which level setting switches are monitored by amicroprocessor. Level changes are loaded into memory, displayed to auser, and implemented by the microprocessor.

Component sound systems are also known wherein system parts, such as aradio, an amplifier, and a cassette tape player, are constructed asseparate integral components which are interconnected duringinstallation into an automobile. The separate components may each bemicroprocessor controlled.

The foregoing prior art systems have disadvantages in bot design andmanufacture. The

h integral units suffer from high cost due to the need for separatedesign efforts and different manufacturing operations. Thus, themanufacture of integral units has not been able to achieve full economyof scale. Component systems suffer these same disadvantages in additionto the disadvantage that they require larger dedicated packaging spacein the automobile than integral units.

Burke et al., U.S. Pat. No. 4,637,022, discloses a mobiletransmit/receive radio having a distributed processing environment. Ashared bus links processors internally and externally. A structuredsubsystem interface is provided such that processors may be added to thesystem without changing the main control processor. Each processor ismodelled as a set of registers which can transmit data to and receivedata from the control processor. Therefore, each local processorrequires nonshared connections to its peripheral devices. Such a systemis undesirable from a manufacturing standpoint due to increased partscount, increased complexity, and reduced reliability. Furthermore, theregister approach in Burke et al. is not readily adaptable to existingmicroprocessor controlled audio sound systems because the addressing andcommanding of the multiprocessors requires the development of a newinstruction set resulting in added design costs.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention toprovide an automotive sound system and method of manufacture whichreduces the costs of design and implementation.

It is a further object of the invention to achieve flexible andsimultaneous manufacture of integral radio receiver and cassette, CD, orDAT sound systems from a common chassis.

It is another object of the invention to provide a pluralmicrocontroller architecture for partitioning each system design into aplurality of interchangeable modules.

These and other objects are achieved in a method for manufacturing anautomotive sound system in which a main board is assembled including amain microprocessor means for performing functions common to a pluralityof selected sound systems. A control board is assembled including asound source mechanism corresponding to at least one of the selectedsound systems and including mechanism microprocessor means forcontrolling the sound source mechanism. The main board and the controlboard are joined and their microprocessor means are connected to acommcn bus. Preferably, the method further includes the step ofassembling a bezel board including operator means for receiving operatorinput and displaying output information and including bezelmicroprocessor means for processing the operator input and the outputinformation. The bezel board is joined to the main and control boardsand the bezel microprocessor means is connected to the common bus.

The invention thus achieves reduced costs and increased flexibility inmanufacture of automotive sound systems through functional andstructural partitioning of the system into bezel, mechanism, and mainchassis modules. The system functions are partitioned in a manner whichminimizes the number of interconnections needed between the modules. Thefinal manufacture of a complete system is accomplished by selecting theappropriate bezel and mechanism modules corresponding to the type ofsystem (e.g., cassette, CD, or DAT) and joining them to a main chassismodule which is preferably common to all system types.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. The invention itself, however, both as to itsorganization and method of operation, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a perspective view of each of the boards and their variantswhich can be assembled to create different sound systems according tothe invention;

FIG. 2 is a functional block diagram of the distributed multiprocessorarchitecture of the invention; and

FIG. 3 is a schematic diagram of a preferred implementation of a portionof the architecture of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a main chassis 10 provides primary radio functionscommon to several different sound systems and provides a structure towhich a mechanism subassembly and a bezel subassembly are attached toform an integral unit. Thus, an integral CD-radio unit can be obtainedby joining CD mechanism subassembly 11 and CD bezel subassembly 12 withmain chassis 10. Similarly, a DAT-radio is obtained by joining DATmechanism subassembly 13 and DAT bezel assembly 14 with main chassis 10,while a cassette-radio is obtained by joining cassette mechanismsubassembly 15 and cassette bezel subassembly 16 with main chassis 10.

Each mechanism subassembly includes a respective mechanism 11a, 13a, and15a for retrieving recorded signals from a particular recorded medium,e.g., CD's, DAT's, and cassettes. Such mechanisms are well known in theart. Each mechanism subassembly further comprises an attached mechanismcontrol board 11b, 13b, or 15b containing the circuitry necessary tooperate the mechanism, including a respective microprocessor 20, 21, and22 and associated memories, input/output devices, and peripherals (notshown) forming respective microcontroller chip sets.

Each bezel subassembly includes a respective bezel front plate 12a, 14a,and 16a, respectively, and an attached bezel board 12b, 14b, and 16b,respectively. The bezel boards include a respective microprocessor 23,24, and 25, and associated chips (not shown). The bezel subassembliesfunction to provide operator interface functions such as system inputs(e.g., volume, tuning, search control) and output displays (e.g.,received frequency, track number, tape direction).

Main chassis 10 has its own main board including a main microprocessor26 and associated microcontroller chips and other devices (not shown) toimplement the radio and main audio functions of the integral soundsystem. Further included on the main chassis are a mechanism connector27 and a bezel connector 28 for interconnecting the respectivemicrocontrollers when the subassemblies are joined to the main chassis.Preferably, the connectors 27 and 28 comprise connections forming acommon bus used by all three microcontrollers with one of themicrocontrollers governing usage of the bus via interrupts.

Turning now to FIG. 2, the distributed control architecture of thepreferred embodiment will be described in more detail. Main board 30,bezel board 31, and mechanism board 32 are interconnected by a commonbus 33. The functional partitioning of the audio system of FIG. 2 isdetermined such that minimum interconnections and communications areneeded between different boards and such that each board can be testedas a stand-alone unit via its bus. Thus, each board preferably includesa complete microcontroller including a microprocessor, memory (RAM andROM), and input/output devices.

Main board 30 performs the functions which are common to a family ofsound systems, i.e., which are indePendent of whether the system is acassette, CD, or DAT. Main board microcontroller 34 keeps a softwaretime-of-day clock (which can be displayed on bezel board 31 as isexplained later). Main microcontroller 34 senses the on/off state of theignition/accessory switch of the automobile such that the sound systemcan be activated only with the ignition/accessory switch on. Main powerto the sound system peripheral devices (e.g., a power antenna) iscontrolled via a line 36 connected to main microcontroller 34. Theoutput of an external audio power amplifier can be muted by mainmicrocontroller 34 by generating a signal on line 37. Microcontroller 34includes a universal asynchronous receiver-transmitter (UART) 38 and acommunication line 39 which provide an RS-232 port to allow remotecontrol and/or testing of main board functions. Although not shown,bezel board 31 and mechanism board 32 may also include such a port.

Main board 30 includes an audio processing section 41 coupled to bus 33and controlled by main microcontroller 34. Audio section 41 receivesplayback sound signals from the mechanism board 32 via a connection notshown or receives radio program signals from a tuner 42 also coupled tobus 33 and controlled by main microcontroller 34. Audio section 41controls system volume, balance, fade, bass level, treble level, andmute. The final audio output is provided from an internal poweramplifier to speakers via a line 43 or, alternatively, as low levelaudio signals to an external power amplifier.

Main board 30 may also include a compression section 44 and a DNR noisereduction section 45 each connected to and controlled by mainmicrocontroller 34 to improve the sound quality of audio signalsprocessed in audio section 41. A read/write anti-theft EEPROM(electrically erasable programmable read-only memory) 46 is included onmain board 30 coupled to bus 46 such that operation of the sound systemmay be conditioned on an exact match between a user entered securitycode and the contents of EEPROM 46 in the event that car battery powerhas been disconnected from the audio system.

Main microcontroller 34 preferably includes a nonvolatile memory forstoring control parameters used by main board 30 such as volume level,tuner frequency, etc. Nonvolatile memorY stores these parameters afterthe system power is turned off so that when the unit is turned back on,the previous settings can be restored.

Considering now bezel board 31, a bezel microcontroller 50 is coupled tobus 33. Bezel board 31 performs all the system functions related tooperator interface such as display of parameters and reading of operatoractuated controls. One or more light-emitting diodes (LED's) 51 areconnected to bezel microcontroller 50 to indicate system status such aspower on. A visual display 52 and display driver 53 are coupled to bus33 and controlled by bezel microcontroller 50 to display informationsuch as time of day, tuner frequency, or track number. Display 52 cancomprise a vacuum fluorescent (VFD) or a liquid crystal (LCD) display,for example.

Operator input devices connected to bezel microcontroller 50 includevolume/tuning up-down switches 54 and an input key pad 55. Inputpotentiometers 56 are coupled to bezel microcontroller 50 via ananalog-to-digital converter (A/D) 57. Keypad 55 can include cassette,CD, or DAT functions, preset radio frequencies, etc., and potentiometers56 can represent audio balance, treble and bass levels, and fade, forexample.

Dimming of visual display 52 is achieved by obtaining a light signalfrom an ambient light sensor or from automobile running light switcheson a "lamps" line 58 which is coupled to A/D converter 57. Bezelmicrocontroller 50 determines an appropriate brightness for display 52and commands that brightness to display driver 53 via a pulse widthmodulator (PWM) 59 and a line 60.

Mechanism board 32 includes a mechanism microcontroller 65 coupled tobus 33. Other components on mechanism board 32 depend on the nature ofthe particular sound system, but can include motor controls for turningtape capstans and spindles or a disk drive, tape head or laser pick-upcontrols, and a digital-to-analog (D/A) converter. Mechanismmicrocontroller 65 controls such functions as loading and ejecting,play, pause, stop, fast forward, rewind, and automatic music search in amanner known to those skilled in the art.

Interaction of the three separate boards depends on an orderly use ofbus 33. Thus, bezel microcontroller 50 supervises all access to bus 33.In order to provide a generic interface between boards and to allowflexibility in changing one board without impacting the design ofanother board, substantially all communications between boards isdirected between microcontrollers. Thus, although bezel microcontroller50 could communicate an increased volume setting directly to audiosection 41, the new setting is instead communicated to mainmicrocontroller 34 which then commands the new volume level.

The bus structure and communication protocol of the invention will bedescribed in connection with FIG. 3, which shows integrated circuitscorresponding to FIG. 2, bus data lines and bus control lines. Bezelmicrocontroller 50 is a system master and may be comprised of an 888CGmicrocontroller manufactured by National Semiconductor. Mainmicrocontroller 30 is a slave of bezel microcontroller 50 and may alsobe comprised of an 888CG. Main microcontroller 30 is master to audioprocessor 41, frequency synthesizer or tuner 42, and EEPROM 46.Mechanism microcontroller 65 is a slave to bezel microcontroller 50 andmay be comprised of a CXP5058 microcontroller manufactured by SonyCorporation.

The microcontrollers are interconnected by a serial bus 33 whichcomprises a master output line 70, a master input line 71, and a serialclock line 72. Clock line 72 provides a timing reference for serialtransfers of data on lines 70 and 71. Line 70 connects the serial dataoutput of bezel microcontroller 50 to the serial data inputs of mainmicrocontroller 30, mechanism microcontroller 65, and display driver 53.Line 70 further connects the serial data input of bezel microcontroller50 to the serial data outputs of main microcontroller 30 and mechanismmicrocontroller 65. Line 71 further connects the serial data output ofmain microcontroller 30 to the serial data inputs of audio processor 41,frequency synthesizer 42, and EEPROM 46.

FIG. 3 also shows bus control lines 73, 74, 75, and 76 for coordinatingthe transmission of commands, messages, and data between bezelmicrocontroller 50 and its slave microcontrollers 30 and 65, accordingto an established, orderly protocol. As system master, bezelmicrocontroller 50 initiates command transmissions to mainmicrocontroller 30 or mechanism microcontroller 65 by first annunciatingan upcoming command using either chip select line 75 or 76,respectively. Conversely, messages or data are transmitted by slavemicrocontrollers 30 and 65 to bezel master microcontroller 50 byannunciating a transfer (and interrupting bezel microcontroller 50) viaservice request lines 73 and 74. After an acknowledgement from themicrocontroller to receive the transmission, the transmission isaccomplished over serial bus 33.

Exclusive access periods to bus 33 are required by main microcontroller30 and are obtained by appropriate commands and messages. Whenever mainmicrocontroller 30 requires use of common bus 33 to communicate with itsslave devices 41, 42, and 46, it must request bus control bytransmitting a "bus mastership request" message to bezel microcontroller50. After granting bus mastership to main microcontroller 30 via a "busmastership granted" command, bezel microcontroller 50 delays servicinginterrupts from mechanism microcontroller 65 or display 53 until mainmicrocontroller 30 relinquishes possession of the bus, as indicated bythe receipt of a "finished with bus" message from main microcontroller30. During the time that exclusive bus access is granted, mainmicrocontroller 30 can communicate with its slaves by signalling aparticular slave over a chip select line 77, 78, or 79.

The foregoing describes an automotive sound system capable of flexible,cost reduced manufacture due to the partitioning of system functionsinto modules. The use of a common chassis for all systems reduces designcost. By providing a generic interface protocol between modules,improvements can be made to individual modules without any impact onother modules

While preferred embodiments of the invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes andsubstitutions will occur to those skilled in the art without departingfrom the spirit of the invention. Accordingly, it is intended that theappended claims cover all such variations as fall within the spirit andscope of the invention.

What is claimed is:
 1. A method for manufacturing an automotive soundsystem comprising the steps of:installing a main board into a chassis,said main board performing audio functions common to a group of playersfor playback of pre-recorded media, said group comprising a cassetteplayer and a compact disc player; selecting a player from said group ofplayers for completing said automotive sound system; installing amechanism sub-assembly corresponding to said selected player into saidchassis, said mechanism sub-assembly including a mechanismmicroprocessor for controlling a player mechanism; installing a bezelsub-assembly corresponding to said selected player into said chassis,said bezel sub-assembly including a bezel microprocessor responsive tooperator inputs and controlling a display for said selected player; andinterconnecting said main board, said mechanicm microprocessor, and saidbezel microprocessor via a common bus.